Although the details of the Z-Machine became well-known in the early
1990s, back in 1982 there was little information available beyond the
Creative Computing article. I wanted to learn more about it, so from
1982 to 1984, I worked on reverse-engineering the Apple ][ ZIP versions
1-3. I produced a commented source file which could be reassembled into
the original object code. I then wrote my own ZIP in Pascal.

Unfortunately I no longer have machine-readable copies of any of my
work, but I do still have a printed listing, which I have scanned.
Of course, it is now only of historical interest.

The code was assembled using a special version of the Microsoft Macro-80
assembler that was part of the A.L.D.S. package for the Apple ][. Macro-80
ran under CP/M, and the normal versions only supported 8080 and Z-80
assembly. But the A.L.D.S. version added support for the 6502, and ran
under CP/M on an Apple ][ equipped with a Microsoft Softcard.

In 1984, the listing file was uploaded to a DECSYSTEM-20 and printed on
a DEC LN01 laser printer (DEC's version of the Xerox 2700).

The Apple II ZIP was written by Bruce Daniels, who was working at Apple
Computer at the time. Bruce was one of the key players in the
development of the Apple Lisa computer; he was responsible for the system
software.